The present invention generally relates to an integrated circuit, and more particularly, to a sensor circuit having a serial interface.
Temperature gradients across the die of today""s high performance very large scale integration (VLSI) components, such as a microprocessor can adversely affect component performance. For example, a temperature variation between two clock driver circuits within a microprocessor often results in system clock skew. Moreover, the die may reach an unacceptable temperature that causes the microprocessor to malfunction or stop functioning.
To protect the microprocessor from thermal damage, a diode is typically placed in the die of the microprocessor to provide a die temperature indication. This diode is driven with a fixed amount of current, and the corresponding voltage drop across the diode provides an indication of the microprocessor temperature. Unfortunately, the diode gives no indication that the diode is operating properly. Moreover, the diode has poor accuracy. The diode provides a temperature reading that is accurate to about xc2x110xc2x0 C.
Because there is only a single diode positioned at a single location on the microprocessor die to measure the temperature of the microprocessor, it is difficult to determine the temperature gradient across the microprocessor. Consequently, early indications that a thermal related problem exists in a portion of the microprocessor are difficult to detect. Moreover, given the need to keep microprocessor pinout density to a minimum along with the surface area of the microprocessor, the use of multiple temperature sensors having interfaces external to the microprocessor is prohibitive.
The present invention addresses the above-described limitations of measuring the temperature of an integrated circuit. The present invention provides an approach to enable a sensor of any type to report a sensed value and to indicate a state of operability via an off chip interface having a minimum number of electrical contacts.
In one embodiment of the present invention, a sensor having a register to hold a response to a sensed physical stimulus and an interface to communicate the response is provided. The sensor communicates the response from the register in a manner that indicates whether the sensor is functioning correctly. The interface is a digital interface having at least two electrical contacts. The first contact receives a trigger to initiate the sense operation and the second electrical contact communicates the sensor response. The sensor communicates its response directly to an apparatus or another integrated circuit, or to another circuit within the integrated circuit the sensor is part of. The sensor provides an absolute or relative value of the sensed physical stimulus. In addition, the sensor communicates via the interface to indicate when the sensor is sensing a physical stimulus.
The above-described approach benefits an integrated circuit that seeks a sensor capable of indicating its operability while keeping the external pin density of the integrated circuit to a minimum. As a result, an integrated circuit can communicate an accurate internal temperature reading from an internal sensor to a device external to the integrated circuit and provide an indication of the sensor""s operability as part of the communication without significantly increasing external pin density of the packaged integrated circuit.
In accordance with another aspect of the present invention, a method is performed in a sensor that indicates a sensor status, a response of the sensor and the sensor""s operational state. By triggering the sensor to sense a physical stimulus, the sensor reports an indication that a sensing operation is in process, a response to the physical stimulus along with a value that is indicative of the sensor""s operational state. The response provided by the sensor has a first portion that is indicative of an absolute or relative value of the sensed physical stimulus and a second portion that is indicative of the operational state of the sensor itself.
The above-described approach benefits a microprocessor architecture that utilizes an active sensor. Because the sensor reports a value indicative of its operational state the microprocessor architecture can be assured that the sensor is operating properly. As a result, the reliability and the confidence of the sensor""s response is significantly increased.
In yet another aspect of the present invention, a sensor that reports a response value and a status value when triggered is provided. The sensor includes a serial interface having one input contact and one output contact. The sensor can be a thermal sensor that reports an absolute or relative temperature value.
In still another aspect of the present invention, a method is performed in a very large scale integration (VLSI) circuit for reporting a temperature sensed by a thermal sensor of the VLSI circuit. By triggering the thermal sensor to sense the temperature of the VLSI circuit the thermal sensor senses the die or package temperature of the VLSI circuit and affixes a value to the sensed temperature that indicates whether the sensor is functioning properly. The thermal sensor reports the sensed temperature value with the affixed value to a device either internal to or external to the VLSI circuit. From the affixed value, the receiving device can determine whether the temperature value provided is reliable or unreliable. Moreover, the thermal sensor of the VLSI circuit can sense and report a temperature of the system in which the VLSI circuit operates.